1. Field of the Invention
This invention relates to an improvement on a distance measuring device based on triangulation and more particularly to an improved distance measuring device which is highly suitable for use in an automatic focusing camera, etc.
2. Description of the Prior Art
Heretofore various kinds of automatic distance detecting methods have been used for automatic focusing cameras. All of these cameras are provided with a distance measuring mark around the middle of a photography picture plane. The main object to be photographed is placed within the distance measuring mark for the purpose of focusing the camera on the main object. However, when the main object is not in the middle of the picture plane, it is always out of focus. A camera of this type is very inconvenient.
Another camera has a pre-focus mechanism wherein, in order for the photographer to have some latitude in composing the picture to be taken, the distance measuring action and exposure action of the camera, which are normally carried out simultaneously, are carried out separately. This type of camera permits photography picture composition with the main object not necessarily located in the middle of the picture. The camera with such a pre-focus mechanism, however, has the following problem:
In a picture composition, as shown in FIG. 1 of the accompanying drawings (having two persons standing with a monument located far behind between them and with an archway of a Shinto shrine farther behind), for example, the photographer, if he is not well versed in cameras, tends to adjust a distance measuring mark A to the monument between the two persons. Then, contrary to the photographer's expectation, the persons are out of focus although the monument is in focus. This kind of failure is a frequent occurrence with such cameras. Thus, conventional automatic focusing cameras have not completely relieved the photographer from focusing operations and have necessitated bringing the main object to the distance measuring mark A.
Furthermore, the ordinary photography composition generally includes a main object such as a person on which the camera should be focused first and an auxiliary object such as a background. Photography with conventional automatic focusing cameras for such picture composition often has the auxiliary object out of focus while only the main object is in focus. There are occasions on which commemorative photography is desired with importance also attached to the background, which is an auxiliary object. On such occasions, the photographer naturally desires to focus the camera on the background as well as on the people who are the main object. However, such a desire has been difficult to satisfy with conventional automatic focusing type camera.
To solve this problem, there has been proposed, in Japanese Laid-Open Patent Application No. SHO 56-101128, a camera with a pre-focus mechanism wherein distance measuring operations are performed, one by one, on a plurality of photography objects. A plurality of data thus gathered is memorized, and then the camera is focused on a point that comprehensively includes all of these objects in an in-focus condition. In accordance with this proposal, the memorized distance information on multiple objects is obtained by computation. The photo-taking lens is adjusted to a focusing position at which all the objects come within the field depth determined by the aperture of the photo-taking lens. Furthermore, in the event that all the object distance information values do not come within the field depth, only the objects that can be covered by the field depth are taken into consideration while the object distance information on the other objects that cannot be covered is cancelled, so that the distance on which the photo-taking lens is accurately focused can be determined.
However, a camera of this type presents another problem in that the photographer is required to repeatedly perform distance measuring operations to bring multiple objects into a distance measuring mark 1. This is not only troublesome but also consuming time. Furthermore, with a automatic focusing camera of this type, in order to have as many objects as possible within the field depth for photographing multiple objects located at different distances within the camera field, the focusing distance of the photo-taking camera is adjusted to a great distance. As a result, it is highly probable that an object which is located close up and which is often the main object to be photographed is blurred while only the background is in focus. This has been a serious problem for the photographer.
A first object of this invention is to provide a distance measuring device capable of simultaneously detecting, by one distance measuring operation, different distances at which a plurality of objects to be photographed are located, so that the above problem of the prior art devices can be solved.
A second object of the invention is to provide a camera having the above device arranged to preferentially permit focusing on the closest object among a plurality of objects subjected to distance measurement.
A third object of the invention is to provide a camera in which the above device is capable of performing a focusing operation, taking into consideration such auxiliary objects as background, etc. in addition to the main object.
A fourth object of the invention is to provide a camera wherein the above device, which is capable of performing a focusing operation while taking into consideration auxiliary objects in addition to a main object, prevents over-exposure of the main object in flash photography.
A fifth object of the invention is to provide a camera which is provided with the above device and which is capable of indicating on what part of the picture plane the photo-taking lens is focused.
The term "focusing distance" as used herein is intended to mean a distance at which the photo-taking lens is accurately focused, i.e. in focus.
These and further objects and features of the invention will become apparent from the detailed description of the preferred embodiments thereof taken in connection with the accompanying drawings.